Apparatus and process for winding under varying tension



March 22, 1966 E. F. BARRETT 3,241,785

APPARATUS AND PROCESS FOR WINDING UNDER VARYING TENSION Filed Jan. '7, 1964 2 Sheets-Sheet l q CONTROLLER C2 22 a U3 \l E I 8 I u CD 0 g a 5 L1 INVENTOR EDWA'RD F. BARRETT AGENT March 22, 1966 E. F. BARRETT 3,241,785

APPARATUS AND PROCESS FOR WINDING UNDER VARYING TENSION Filed Jan. 7, 1964 2 Sheets-Sheet 2 E w- 5 i 56 g 2' 0- g 48- WIND UP ROLL LENGTH (FEET) 0AM POSITION IN DEGREES INVENTOR woo EDWARD E BARRETT BY 7km. 6. Cw,

AGENT United States Patent 3,241,785 APPARATUS AND PRGCESS FUR WlNDlNG UNDER VARYENG TENSIUN Edward F. Barrett, Monroe, Conn, assignor to E. l. du

Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware Filed Tan. 7, 196 3, Ser. No. 336,183 12 Claims. (Cl. 242--'l5.51)

This invention relates to a device for improving the programming of web tension. More particularly this invention relates to a device for automaticaily programming web tension as a function of web footage to achieve the optimum tension profile while winding a web upon a mandrel.

In the manufacture of photographic film, paper, plastic film, fabrics, etc., material in web form is wound on cores. The formation of the wound web is dependent upon the tension of the web, and if the correct tension is not maintained the wound web will be defective, i.e., cinches or telescoping will occur.

Control of the formation of a Wound web is most important during the first few laps as any defect at this stage will be accentuated during the winding of the re mainder. At the beginning, the core diameter may be a few inches, whereas .at the finish its size will be many times of that of the core, i.e., in the order of three to six times core diameter. These differences in diameter from the start to finish create problems with respect to maintaining the correct tension on the Web to form a roll of good quality.

In applications where the wind-up takes place with a constant tension, a shifting of the edge profile of the Web on the core occasionally occurs. These sudden shifts are the result of the axial shifting of the core relative to the rest of the roll, or the shifting of the inner Wraps of the roll relative to the rest of the roll. With constant tension the inner wraps are wound with the tension acting through a relatively small moment arm and as the size of the Wound-up roll increases, the moment arm increases. Thus the force acting on the inner wraps is much greater at the later stages of roll formation. Attempting to later transmit this greater force through the previously wound wraps causes the latter to be tightened and shift axially.

It has also been found in practice that the use of constant torque winding also does not provide the most suitable operational features. With constant torque winding, the tension at the end of the Winding is several times less than that at the start, i.e., the tension change is approximately inversely proportional to the diameter of the windup roll. Thus most constant torque rewinds are limited to a 3:1 ratio of roll to core diameter, and if the roll diameter exceeds 3 times core diameter the torque is decreased to such an extent that the outer layer becomes too loose to continue winding.

What is desired in a rewind operation is a method that varies the tension to obtain the best roll profile, such as a method that initially has a high tension which is gradually reduced as the rewind roll builds up, but maintains suflicient tension to wind the outer layers of the roll.

Accordingly, it is an object of this invention to provide a device for tension control that can be used when the relationship of web length to tension is critical and must be varied in other than a constant torque or constant tension pattern. Another object of this invention is to provide a device for automatically programming web tension by varying the tension relative to web footage and reproducing the same program automatically for subsequent webs. A further object is to program web tension 3,2dlfld5 Patented Mar. 22, 1966 'ice according to a prior determined pattern and thereby obtain a tapered tension between the start and finish of a winding operation. A still further object is to provide a method that improves a web rewinding operation by allowing the web tension to vary according to increases in rewind web roll size as determined by the length of web to be wound.

A still further object is to provide a device that will automatically adjust to give the correct web tension for a specified length of web being wound on a mandrel. Other objects will appear hereinafter.

These and other objects are accomplished by the invention as disclosed in the appended claims.

The apparatus of this invention is useful in all Web operations where the tension must be controlled at a programmed rate, i.e., in the winding of webs of film, paper, woven and nonwoven fabric, and it is particularly useful in the winding of photographic products. In the latter operation, cast base or coated base is wound on mandrels for storage or for transport. The coatings on such webs are sensitive to pressure and deformation, thus narrow limits of tension must be maintained. If, during the winding, too low a tension is used, a soft roll is produced and defects occur. If the tension is too high, a hard roll is produced and results in pressure marks or lap marks.

The invention is best explained by means of the attached drawings which are part of this specification and in which:

FIGURE 1 is a schematic diagram of a preferred embodiment of this invention.

FIGURE 2 is a curve of an optimum tension profile for a particular Web.

FIGURE 3 is the contour of a cam machined to the curve of FIGURE 2.

The preferred embodiment of the apparatus of the invention involves means for converting web footage into electrical pulses that step a synchronous motor. The rotation of the stepping synchronous motor determines the position of a cam with a contour machined to represent the desired tension relative to web footage. A pneumatic means senses the contour and develops a pneumatic signal that is representative of the desired tension with respect to footage. The pneumatic signal is the set point for a pneumatic feedback tension control system that has a tension detector for creating a signal representative of the actual web tension which is compared with the set point in a controller and any differential between the two signals is used to regulate the tension on the web.

More particularly, a moving web 16 of flexible material is made to pass over an idler roll 11. The movement of the Web produces a proportional rotation of the idler roll. Ideally, the circumference of the idler roll would be the unit of measure used for the web, in the case of photographic films it might be one foot, thus one rotation of the rollwould equal one foot of the web. A cam 12 is mounted on the shaft of the idler roll so they will rotate together. A microswitch 13 in an AC. circuit is operated on by the cam, i.e., the cam closes the contacts of the switch with each revolution of the idler roll. The switch 13 is arranged to impress v. AC. across the coil of a relay 14- each time the cam closes the contacts. The pulsing A.C. input into the coil operates on relay contacts wired to a 25 v. 13.0 supply and produces a pulsing DC. output, i.e., one pulse per web foot.

The pulsing DC. output is the input signal to a synchronous motor control unit 16 or translator. This unit is a pulse to step converter and produces 11C. pulses of the opposite polarity that are applied to the field windings of a synchronous step motor 17 in the proper sequence. The sequence of DC. pulses moves the rotor of the motor around the stator in discrete steps, i.e., a certain number of steps per revolution. Thus the web footage has been converted to the proportional rotation of the synchronous stepping motor 17.

A motor control unit or translator that can be used is the type ST250 SLOSYN translator manufactured by Superior Electric, Bristol, Connecticut; the operation and construction of this unit is described in their bulletin SS361-1, copyrighted in 1962. The Model 150-1010 SLOSYN synchronous motor also made by Superior Electric and described in their bulletin SS459, copyrighted 1959, and in US. Patents 2,982,872 and 2,931,929 can be used as the stepping motor.

In some situations it may be necessary to remove excess A.C. noise from the motor control circuitry. This may be done by adding a shunting capacitor across the input terminals. The valves of the components of the noise filter shown are typical and may have to be altered to suit the characteristics of the particular unit involved.

The stepping movement of the rotor of the synchronous motor is directly connected to a planetary gear train 18. The gear train connects the rotation of the synchonous motor to the rotation of a contoured. cam 19 which serves as a memory device. The gear train is a reduction gear designed to provide a rotation of less than 360 for the length of web involved, e.g., with a web length of 4000 feet the gear train could provide a cam rotation of 270.

The output of the gear train is connected to the contoured cam by the engagement of a magnetic clutch 20. During operation the magnetic clutch is energized and the output of the gear train is connected to the cam 19. At the end of each web, the magnetic field of the clutch is broken and the clutch will disengage. The input to the clutch from power supply 21 is regulated. by a switch 22. This switch can be manually operated when the rewinding of a particular web is completed or appropriate means (not shown) can be installed to open and close the switch automatically upon the completion of one web and the start of a new web. When the clutch is disengaged, a weight 23 on the cam will cause it to rotate to the starting position, which is located by a mechanical stop 24.

The contour of the cam 19 is machined to the curve of the desired tension with respect to web footage. The optimum tension profile for the type and length of web involved can be determined experimentally and a curve developed. For example, FIGURE 2 shows the experimentally determined curve of the optimum tension profile for winding a 45-inch wide, 3000-foot long web of photographic film about .007 inch thick. Also indicated is the cam 19 position in degrees in relation to web footage. Using the data from FIGURE 2 a cam can be machined with a contour that represents the desired tension with respect to footage. FIGURE 3 shows the contour of a cam machined from the curve of FIGURE 2. It is ob vious that the cam will be useful for the particular type and length of web for which it was designed and if the web is varied it may be desirable to have another cam of appropriately designed contour. Thus by the method of this invention any relationship of web footage to winding tension may be obtained by using an appropriate cam contour.

The contour of the cam is sensed by a weighted follower 25 of a pneumatic position transmitter 26, such as a Foxboro Type CP Position transmitter, described in Book No. 1612 published by Foxboro Company, Foxboro, Mass. The pneumatic output signal of the position transmitter is representative of the desired tension for the particular web footage that is passing over the idler roll and is the set point signal that can be introduced into the pneumatic controller 27 of a tension control circuit.

The conversion of web footage into a cam position and the developing of a control signal representing the desired tension with respect to footage can be accomplished by other means without departing from the spirit of the invention. For example, the idler roll 11 could be marked axially with a dark line. As the roll rotates, each time the line passes a certain point it would be sensed by a photoelectric cell and an impulse developed. The impulse could be used to step a motor as previously explained In addition to the profiled cam, any memory device such as programmed tapes which move in a pre-arranged relationship with the web movement can be used to issue a set point signal corresponding to the desired tension for a particular Web.

In the illustrated tension control circuit, the actual tension in the web is sensed by hydraulic means and pneumatic feedback means are used to develop a correcting signal that is sent to the final control element. The tension on the web is measured by a roller 28 that is located in close proximity to the footage sensing roller 11 so that the desired footage and tension relationship can be obtained. The bearings for the roller are mounted on top of two hydraulic-load cells 29. The load cells are force measuring devices and work on the principle that the hydraulic fluid in the system is retained at a fixed volume and that any hydraulic pressure produced is proportional to the force applied to the cell through. the bearings. The preferred embodiment uses two load cells on the roller. It is known that in many applications the tension on one side of a web will vary from the tension on the other side and the tension sensed by a load cell on one roller end is not representative of one-half the tension in the web. The sum of the tension sensed by the two load cells on the roll will, however, be a true indication of the actual web tension at that particular roll.

The hydraulic pressure in the load cells is sent through capillaries 30 to hydraulic-pneumatic transducers 31. The damping action of the capillaries insures that noise in the hydraulic system due to bearings, rolls and web flutter will not be present during the transmission of the pressure. The transducers work on the principle of null balance of forces. Any change in the hydraulic pressure will act on a hydraulic bellows in the transducer and will produce a pneumatic balancing pressure that is equal and opposite to the force of hydraulic bellows. The transducer produces an output signal that is in the range of 3 to 15 p.s.i. and is compatible with most pneumatic instruments. The operation and construction of a hydraulic load cell is disclosed in US. Patent 2,960,113 and that of a hydraulic/pneumatic transducer in US. Patents 2,312,201; 2,359,236; and 2,501,957.

The pressure signal from each load cell is converted into a pneumatic signal in the appropriate transducer and all the converted signals are sent to a totalizing relay 32. This relay adds the two input signals and develops a signal that is representative of the total measured tension in the web. A relay that may be used is the Moore Products Nullmatic M/F Relay, Model 68-3, a description of which may be found in Bulletin AD68, published by Moore Products and copyrighted in 1961. The output signal of the totalizer may be recorded by a standard, 2- pen pneumatic 3-15 p.s.i. recorder 33. The recorder having impulse chart drive with its drive synchronized with web footage so it records in terms of tension and web footage.

The pneumatic proportional plus integral controller 27 receives both the set point signal from the cam follower and the signal representing the actual tension in the web. The controller in analog fashion computes a signal based upon the time integral of the amplified difference between the two inputs. A controller that can be used is the Moore Products Nullmatic Controller Model 56MF, a description of which may be found in Bulletin 5018 published by Moore Products and copyrighted in 1962.

The controller output signal is sent through an inverse derivative unit 34 where violent or sudden variations in the signal are smoothed out. This unit causes the changes in the signal pressure to occur over a period of time sufficient to reduce the rate of pressure change. A description of such a unit may be found in U.S. Patents 2,431,297 and 2,501,957. The output signal is then amplified in a 1:3 booster pneumatic amplifier relay 35. This relay 35 supplies a controlled pressure input to control the torque of a pneumatic motor 36 that drives the re-wind mandrel 37. The controlling of the torque of the motor controls the tension in the web, i.e., a change in the torque will produce a proportional change in web tension. If desirable, the automatic control unit could control the torque of the un-wind mandrel, whose torque also affects the tension on the web.

Many other automatic tension control systems or units may be used with the method of the invention. For example, the web tension could be sensed by pneumatic load cells or electrical strain gauges and proportional signals developed. The signal representing the actual tension on the web could be compared with the set point signal by various means, such as a hydraulic totalizing relay, electrical summer circuits, electrical controllers, and a correcting signal thereby developed. This signal could be sent to a final control element that would control the tension on the web, e.g., an un-wind motor or brake or a re-wind motor or brake.

The system of this invention is independent of speed (except for a slight lag in control response during acceleration). This novel apparatus is capable of winding webs to identical tension patterns regardless of the thickness of the web. This is accomplished by having the tension regulated automatically by changing winding torque to a value that will result in the desired tension.

What is claimed is:

1. A device for varying the tension upon a predetermined length of web being wound which comprises (A) drive means for moving said web;

(B) means for counting the passage of specified footage of said web and producing a signal for the passage of said footage;

(C) means for converting said footage signal into movement of a memory device which has been pro grammed to issue a signal representing the desired windup tension upon said web for any given footage of said predetermined length of web;

(D) tension detector means for sensing and signaling the actual web tension for said given footage of said length of web; and

(E) control means to compare said programmed signal and said detector signal and issue a signal equivalent to the differential of said two compared signals which effects the output torque of said drive means.

2. A device for varying the tension upon a predetermined length of web being wound around a mandrel which comprises (A) means for counting the passage of a specified footage of said web and producing a signal for every passage of said footage of web;

(B) means for converting said signal into segmented rotation of a contoured cam in a manner that said cam completes no more than one revolution during the passage of all of said web which is to be wound thereby allowing said cam to be contoured to represent the desired web tension to correspond to a particular specified length of said web;

(C) cam follower means for converting said cam position into a signal representing the programmed tension for the particular section of said web represented by the point upon which said follower is registering;

(D) tension detector means for signaling the actual web tension for said given footage of said length of web;

(E) controlling means to compare the signals from said follower and detector and issue an output signal- (F) means for winding said web which is responsive to said output signal by changing the winding torque thereby resulting in the desired tension on said web.

3. An apparatus for winding a web of a predetermined length while changing the tension upon the web which comprises (A) a motor;

(B) a windup mandrel for said web driven by said motor;

(C) programmed means for issuing a signal corresponding to the desired tension to be exerted upon said web based upon the length of said web which has been wound on said mandrel;

(D) tension detector means for issuing a signal for the actual tension upon said web; and

(E) control means for comparing said programmed and detector signals and issuing a corrective signal for any difference between said signals, said corrective signal effecting a change in the output of said motor.

4. An apparatus as defined in claim 3 where said programmed means is a cam and cam follower, said cam making no more than one revolution during the time said length of web is completely wound.

5. An apparatus as defined in claim 3 where said tension detector is a hydraulic detector.

6. An apparatus for maintaining a variable tension upon a predetermined length of web being wound upon a mandrel comprising in combination (A) programming means to give a variable signal representing the desired variable tension upon said web for the complete length of web as it is being wound;

(B) tension detecting means to give a signal representing the actual tension upon said web; and

(C) control signaling means for determining any difference between said programming signal and said signal from said tension-detecting means and issuing a control signal equal to said difference for governing the torque of said mandrel.

7. An apparatus as described in claim 6 where said programming means comprises a cam and cam follower whereby said cam completes no more than one revolution during the time necessary to entirely wind said length of web and said cam is profiled to translate the desired tension data for any particular footage of said web as a signal through said follower.

8. An apparatus as described in claim 6 where said tension detecting means is a hydraulic detector.

9. An apparatus as described in claim 6 where said tension detecting means has hydraulic cells transversely located to the movement of said web.

10. An apparatus for winding 9. web of predetermined length while changing the tension upon the web, which comprises in combination (A) a drive motor;

(B) a mandrel operated by said drive motor for winding said web;

(C) footage counting means for signaling the passage of designated segments of said web;

(D) a stepping motor responsive to said footage signals;

(E) means for reducing the shaft rotation of said stepping motor so that the shaft rotation will cause a cam connected to said reducing means to complete no more than one rotation;

(F) a cam connected to said reducing means said cam being machined to represent the desired tension upon said web with respect to web footage;

(G) cam follower means for converting the position of said cam into said desired tension signal;

(H) a hydraulic tension detector to measure the actual tension upon passage of said web and issuing a signal representing said actual tension; and

(I) means for comparing said detector signal and cam follower signal and then transmitting a corrective signal corresponding to the differential of said detector and cam follower signals which corrects the torque output of said drive motor, thereby eifecting the tension on said web.

11. A method for winding a predetermined length of web on a mandrel while varying the tension on said web which comprises (A) issuing continuous programmed signals corresponding to the desired tension upon said web as the web is being wound;

(B) measuring the actual tension upon said web as the web is being wound;

(C) comparing said programmed and measured tension to obtain a signal representing any differential in tension; and

(D) changing the output of a drive motor for said mandrel upon receipt of said difierential signal thereby correcting the tension upon said web.

12. A method for winding a predetermined length of web on a mandrel while varying the tension on said web which comprises (A) creating a signal upon the passage of specified footage of said web;

(B) moving a programmed memory device on receipt of said footage signals;

(C) sending a signal from said device which represents the desired web tension upon the web at the point corresponding to the web footage creating said footage signal;

(D) measuring the actual tension on said web at the footage point which causes said desired tension signal to be transmitted;

(E) determining any difference between said actual web tension and said desired tension signal to create a corrective signal; and

(F) correcting the output torque of a drive motor for said mandrel by said corrective signal thereby effecting the tension upon said web.

References Cited by the Examiner UNITED STATES PATENTS 2,353,408 7/1944 Larsen 242-7551 2,978,200 4/1961 Larsen et a1. 242--75.51

MERVIN STEIN, Primary Examiner. 

3. AN APPARATUS FOR WINDING A WEB OF A PREDETERMINED LENGTH WHILE CHANGING THE TENSION UPON THE WEB WHICH COMPRISES (A) A MOTOR; (B) A WINDUP MANDREL FOR SAID WEB DRIVEN BY SAID MOTOR; (C) PROGRAMMED MEANS FOR ISSUING A SIGNAL CORRESPONDING TO THE DESIRED TENSION TO BE EXERTED UPON SAID WEB BASED UPON THE LENGTH OF SAID WEB WHICH HAS BEEN WOUND ON SAID MANDREL; (D) TENSION DETECTOR MEANS FOR ISSUING A SIGNAL FOR THE ACTUAL TENSION UPON SAID WEB; AND (E) CONTROL MEANS FOR COMPARING SAID PROGRAMMED AND DETECTOR SIGNALS AND ISSUING A CORRECTIVE SIGNAL FOR ANY DIFFERENCE BETWEEN SAID SIGNALS, SAID CORRECTIVE SIGNAL EFFECTING A CHANGE IN THE OUTPUT OF SAID MOTOR. 